President Bill Clinton masterminded a "multi-faceted scheme to obstruct justice" over his relationship with Monica Lewinsky for which he should be thrown out of office, the United States Senate was told at the start of the impeachment trial in Washington yesterday.

"We are here today because President William Jefferson Clinton decided to put himself above the law, not once, not twice, but repeatedly," Congressman James Sensenbrenner told the 100 senators who hold the president's fate in their hands.

As the Senate and the American nation began its journey into the constitutional unknown, the defendant in the so-called "trial of the century" chose to visit a police station in neighbouring Virginia to celebrate the latest improvement in the crime figures and to make a speech about community policing, announcing higher law enforcement spending.

Mr Clinton made no comment about the impeachment trial, which he does not intend to attend.

He was one of the few members of the US political establishment who did not spend yesterday glued to the events in the Senate chamber, where the senators sat meek and silent at their desks, forbidden to speak while the trial continues and issued with a reminder to switch off their pagers and cellphones as the proceedings go on.

Washington watched with a mixture of awe and disbelief as the chief justice, William Rehnquist, called the Senate to order just after 1pm on a grey, cold January afternoon to launch the only impeachment trial of an elected US president in the nation's 220-year history.

"The Senate will convene as a court of impeachment. The chaplain will offer a prayer," Chief Justice Rehnquist announced, before the Rev Lloyd Ogilvie led the senators in a prayer imploring: "Dear Father, help us through this difficult time."

With the main US television networks except Rupert Murdoch's Fox Channel covering the proceedings live, Henry Hyde, the chairman of the House of Representatives judiciary committee, introduced the perjury and obstruction of justice impeachment articles against Mr Clinton. Mr Hyde and his 13 trial "managers" have three days to set out their case.

The key issue on this "solemn and historic occasion", Mr Hyde said, was the sanctity of the presidential and legal oaths which Mr Clinton had sworn to uphold. Drawing on Robert Bolt's play A Man For All Seasons, Mr Hyde quoted Sir Thomas More saying: "When a man takes an oath, Meg, he is holding his own self in his hands. Like water. And if he opens his fingers, then he needn't hope to find himself again."

Mr Hyde gave way to a succession of colleagues who outlined the facts relating to the two charges. Further presentations will be made on the law today and tomorrow.

There were increasing signs of strain in the bipartisan atmosphere among Washington's lawmakers now turned presidential jurors. Democratic senators began the day by protesting that Republican leaders had breached a procedural pact to delay a decision on possible trial witnesses against Mr Clinton by allowing their senators to hold private talks on the subject with party colleagues from the House of Representatives who are bringing the case against Mr Clinton.

The Democratic Senate leader, Tom Daschle, said: "It certainly violates the spirit of the agreement that we just all agreed to last week."

The issue has emerged as the crucial divide between the two parties and will be resolved in 10 days when the 100-member Senate votes on whether to hear from Ms Lewinsky and other witnesses. The unresolved dispute over witnesses came to the surface several times in Mr Sensenbrenner's speech as he pressed the senators to accept that a trial without witnesses would not command public support.

Mr Clinton's lawyers, who sat listening to the prosecution presentation at a specially built table in the well of the Senate yesterday, will begin their case on Monday, at the start of three days of defence argument.